1. Field of the Invention
The invention relates to a control apparatus for an internal combustion engine. In particular, the invention relates to a control apparatus for an internal combustion engine that performs engine stop control.
2. Description of the Related Art
As a related art, as disclosed in, for example, Japanese Patent Application Publication No. 10-317936 (JP-A-10-317936), there is known a control apparatus for an internal combustion engine that is configured to hold a ratio of injected fuel that has been mixed with lubricating oil (an oil dilution ratio) low. In the related art, when the necessity to reduce the oil dilution ratio arises, the temperature of coolant for the internal combustion engine is raised to raise the temperature of lubricating oil, thereby promoting the evaporation of the fuel that has been mixed with lubricating oil.
Further, as another related art, there is known a control apparatus for an internal combustion engine that performs so-called engine stop control. In engine stop control, when the output of the internal combustion engine is not required; the operation of the engine is temporarily stopped. As examples of engine stop control, idle stop control for stopping the internal combustion engine when a vehicle is stopped at a traffic light or the like, control for stopping the internal combustion engine when a hybrid vehicle runs by an electric motor, and the like are known.
Meanwhile, the aforementioned related arts adopt a configuration in which the oil dilution ratio is held low by controlling the temperature of lubricating oil on the basis of the temperature of coolant for the internal combustion engine. However, the following problem is caused when these related arts are applied to a vehicle in which engine stop control is performed.
When engine stop control is performed during the operation of the internal combustion engine, the combustion in the internal combustion engine as a heat generation source in a cylinder is stopped. Thus, the temperatures of a cylinder bore and lubricating oil tend to fall more rapidly than in the case where the combustion of the internal combustion engine continues. Then, when the temperature of oil suddenly changes, the relationship between the temperature of oil and the temperature of coolant also changes greatly. Therefore, it is difficult to estimate or control the oil temperature on the basis of the coolant temperature. As a result, the control of the oil dilution ratio is also likely to undergo an error.